1. Field of the Invention
The present invention relates to an audio and video multiplexed transmission system, and more particularly, to a multiplexed transmitter and/or receiver for transmitting and/or receiving audio and video information by effectively coding and/or decoding the audio and video information and performing a multiplexing and/or demultiplexing according to the transmission rate of a communication channel which is a limited transmission medium.
2. Background Art
Recently, an apparatus for simultaneously transmitting audio and video information for communication, such as a video conference system and a videophone, has been developed. In the multiplexed transmission system, a technique is required for coding/decoding information with high efficiency while maintaining balance of the audio and video information. In detail, coded video information occupies a greater amount of data compared to coded audio information. Thus, when transmitting audio and video information at the same time, the transmission rate at a communication channel is limited, and coding and decoding times become different, so that it is difficult to synchronize the audio and video information.
To solve this problem, a method using two transmission channels is used: one for video information, and the other for audio information. However, two transmission channels are required. Also, there is a method using one transmission channel. However, according to the method using one transmission channel, extra logic is required in a transmitter for calculating the delay time of the video information, and logic is required in a receiver for delaying the audio information by as much as the delay time of the video information. Also, there is a method for simultaneously transmitting lip-sync information, based on the MPEG-2 standard for the synchronization of the video and audio information. However, it is difficult to implement hardware for the method for transmitting the lip-sync information, and impossible if the transmission speed of a transmission medium is slow. MPEG is a compressed audio/video signal protocol established by the Moving Pictures Experts Group of the International Standardization Organization. An example of a MPEG coding system is provided in U.S. Pat. No. 5,751,356 to Hiroshi Suzuki entitled Video/Audio Signal Coding System. Additionally, an example of a MPEG decoding system is provided in U.S. Pat. No. 5,621,772 to Greg Maturi et al. entitled Hysteretic Synchronization System ForMPEGAudio Frame Decoder.
A further example of the prior art, which is related to the present invention, is U.S. Pat. No. 5,231,492 to Ryoichi Dangi et al. and entitled Video And Audio Multiplex Transmission System. The U.S. Pat. No. 5,231,492 patent discloses a multiplexed transmission system for audio and video information which is capable ofproviding optimum quality video and audio information. However, extra coding/ decoding of the video and audio information is performed under the control of a controller, so that it is difficult to overcome a time delay between the video and audio information. Thus, it is difficult to achieve exact synchronization between the video and audio information. Also, due to the difference in transmission rates between the video and audio information, it is also difficult to achieve an effective transmission while conforming to a channel transmission rate.